Thats the way tesla voice calling has always worked for me (the way you describe). It doesnt seem to take into account if your contact has multiple numbers, but you say the tag after it (like "so and so mobile" or "so and so work"). it just pulls up that list which isnt helpful if you are voice calling because you are driving.
There are only a couple of work arounds for this that I am aware of, but perhaps others have more.
1. dont use the tesla voice command, use the one from your cellphone (siri / hey google etc).
2. Create new contacts for your most used, that only have one phone number in it.
I dont like technology "auto listening" to me (its a personal choice) so I dont have an amazon alexa, nor do I have "hey siri" / "hey google" enabled to be voice activated. When I use those commands on my smartphones, I have to push the button to activate them (so that means option 1 doesnt work for me, although I did test it a while ago to see if it the workflow would work in the car, and it does).
So, I did #2, creating a separate contact for a few people I might call while I was driving, with the phone number I would call them (and only that phone number).
I dont know if there is any other work around for this, perhaps someone else has one.